It sounded like something from an episode of “The X-Files”: Starting a few weeks ago, in a suburban neighborhood a few miles from a NASA research center in Ohio, garage door openers and car key fobs mysteriously stopped working.

Garage door repair people, local ham radio enthusiasts and other volunteer investigators descended on the neighborhood with various meters. Everyone agreed that something powerful was interfering with the radio frequency that many fobs rely on, but no one could identify the source.

Officials of North Olmsted, a city just outside Cleveland, began receiving calls about the problems in late April, Donald Glauner, the safety and service director for North Olmsted, said on Saturday.

In the weeks that followed, more than a dozen residents reported intermittent issues getting their car fobs and garage door openers to work. Most lived within a few blocks of one another in North Olmsted, though some were from the nearby city of Fairview Park.

Not every car fob failed to work, said Chris Branchick, whose parents live in North Olmsted. He said that whenever he visited his parents in his GMC vehicle, the fob would not unlock the car door; if he went in his fiancée’s Nissan, things were fine.

“We thought maybe it was a foreign versus domestic thing,” he said.

Officials from the cable company and AT&T joined the search for answers, and on Thursday, the Illuminating Company, a local electric utility, dispatched inspectors to investigate.

“They began by shutting off the power in the places where they detected the strongest reading for interfering radio frequencies,” said Chris Eck, a company spokesman. But even after shutting off power on an entire block, the overpowering frequency persisted.

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Wanda Walker, right, holding the door as Anna Walker carries her daughter out of their car. For weeks the Walkers said the key fobs for their car would not work at home but would work outside of their neighborhood.CreditDustin Franz for The New York Times

Dan Dalessandro, a television repairman, was one of several ham radio aficionados who went to investigate. At first, he said, all he picked up were “little blips” on a signal detector, but on one block — and at one house in particular — the signal was extraordinarily powerful.

By Saturday afternoon, City Councilman Chris Glassburn announced that the mystery had been solved: The source of the problem was a homemade battery-operated device designed by a local resident to alert him if someone was upstairs when he was working in his basement. It did so by turning off a light.

“He has a fascination with electronics,” Mr. Glassburn said, adding that the resident has special needs and would not be identified to protect his privacy.

The inventor and other residents of his home had no idea that the device was wreaking havoc on the neighborhood, he said, until Mr. Glassburn and a volunteer with expertise in radio frequencies knocked on the door.

“The way he designed it, it was persistently putting out a 315 megahertz signal,” Mr. Glassburn said. That is the frequency many car fobs and garage door openers rely on.

“There was no malicious intent of the device,” he said in a statement.

The battery on the device was removed and the signal stopped. “It was a relief,” Mr. Glassburn said.

More broadly, the case is a reminder of the power of radio frequencies, Professor Wandt said.

“They are not inherently dangerous to a human being,” he said. “But they could cause mass chaos in our technologically advanced society in ways we cannot predict.”